According to the United Nations human settlements programme, UN Habitat, Africa is the fastest urbanising continent in the world. By 2050, 60% of all Africans will be living in cities.

But urbanisation in Africa is not going hand-in-hand with widespread economic growth: many cities are in fact seeing a proliferation of urban poverty. Food insecurity and undernutrition is therefore also increasingly an urban issue, and with urban people more dependent than rural populations on whatever food they can afford to buy, it's tied closely to livelihoods.

A new project by the World Vegetable Centre (AVRDC) is trying to address this by pulling together the issues of urban growth, migration, livelihoods and undernutrition, and drawing specific attention to the role of peri-urban 'corridors' of production outside cities.

"Populations in general are growing very rapidly in Africa, and on top of that we're seeing increased urbanisation," says Mellissa Wood, director of the AIFSRC.

"But young people in cities are not necessarily finding employment opportunities, and that is potentially increasing future food security issues in these regions. This project is quite holistic, so it's getting young people into vegetable production as a source of livelihoods, helping existing farmers too, and optimising the whole system by finding improved varieties that will work well in particular regions, and strengthening value chains."

The main vehicle for the project is the establishment of best practice hubs in peri-urban areas – which it defines as areas within 2-3 hours of cities – around the four target cities. These hubs will serve as centres for crop trials and experimentation, and will give the young producers who are new to farming full training in vegetable crop growing and management. They will also be open to existing farmers looking to improve their skills, so the idea is that they will serve best practice sites for the farming communities around them.

The project aims to train 120 young people in each of the four countries, and to reach about 6,000 farming households through open participation and farmer-to-farmer diffusion.

"We're going to provide training across the vegetable value chain, from seed production to harvest and marketing," says Victor Afari-Sefa, project leader at AVRDC.

"The hubs are designed to fill knowledge gaps. Some farmers in peri-urban areas use waste water for their crops, for example, which is a major issue. And there is pesticide misuse, with farmers getting frustrated and spraying anything to kill pests. These are some of the things we want to address."

Existing peri-urban producers may have proximity to cities but don't necessarily have market access to sell to buyers there, so it's thought that by locating the hubs in these areas and providing marketing support, the project will be able to build stronger value chains between peri-urban and urban areas. This could improve the livelihoods of participating producers – including the new groups of young trainees – while also improving supplies to urban populations of some of the most productive and nutritious cultivators of traditional African vegetables such as Ethiopian kale and amaranth.

"To date there's been lots of emphasis on growing staple crops like rice and maize for their calorific content, to get food into people's stomachs," says Wood.

"This is necessary, but in the areas this project is working in there are high levels of childhood stunting. It's not necessarily a lack of calories, but a lack of micronutrients and vitamins because the diet is not diverse. So we were interested in this project because it's also focusing on nutrition-sensitive agriculture."

Building the livelihoods and capacity of a few thousand peri-urban producers isn't going to solve the challenges of urban food and nutrition insecurity on its own. But according to Marielle Dubbeling, director of the Ruaf Foundation, a research network for urban agriculture and food security, it's encouraging to see more nuanced recognition of urban, peri-urban and rural food systems in development discourse.

"There's still a heavy focus on rural food production, and we can see that in international declarations, such Rio+20, where urban food security is hardly mentioned," she says.

"And too often, urban and peri-urban are grouped together. Not just that, but also the different types of urban and peri-urban agriculture. Urban agriculture is community gardening but also rooftop gardening, or allotments along roadsides, and there are also many types of peri-urban agriculture. All these types require different policy and support mechanisms. Rooftop gardening requires that you look into building codes, for example, and the carrying capacity of the roof. And dairy farming in peri-urban area requires other policies than large-scale horticulture in those areas."

At the same time, urban or peri-urban food security policies also need to consider how the livelihoods of the urban poor do not exist in geographical isolation. Particularly in the context of migration, urban and rural livelihoods span the physical divide.

"And in many cases this overlaps with migration and remittances, as migrants typically send money back to rural relatives to invest in education or changes in production and so on."

As cities in the global South continue to expand, policy that is sensitive to this interplay and to the different roles of urban, peri-urban and rural agriculture is something that may become increasingly important in ensuring urban food and nutrition security. This is where development organisations could contribute, says Dubbeling.

"I think there is a real need for policy advice. Cities need policy advice, and support in how to assess their urban food system, how to plan for it and implement it. They need financial support, and ways of exchanging information, and peer learning. At city levels there will be differentiation of what they need to support; that's what food policy councils are already doing in many cities in the US and Europe. And we're starting to see that in cities in the global South now too."